Lecture1

Nick Bloom, Stanford University, Labor Topics, 2015 1

LABOR TOPICS

Nick Bloom

Skill Biased Technical Change (SBTC)


Why care about skill-biased technical change?

It is a major topic in the literature – over 100 papers in the last two decades.

There are a number of outstanding questions on this that careful micro-data work can address

Key political phenomena – Governments around the world have faced criticism that their economic policies have increased earnings inequality


Even at the AEA


Why this SBTC occurred


Changes in wage equality


Wage inequality over time

Source: Autor, Katz and Kearney (2008, RESTAT)


Wage inequality has been rising over timeIn the US wage (and consumption) inequality has risen since the 1960s

Note the fall in female wage discount despite rising labor participation



What about by education: college/high school


Residual inequality is the variance of the error term (ei,t) from a Mincer wage equation: Log(wi,t) = α+βtXi,t+ei,t


This occurred throughout the period from 1960s


Note: The CPS data is available both from the NBER data section, and Census data from the Michigan IPUMS data site.

Residual inequality is the variance of the error term (ei,t) from a Mincer wage equation: Log(wi,t) = α+βtXi,t+ei,t


This increase in inequality was particularly a phenomena of the top half of the earnings distribution









Inequality also rising across educational groups


In a standard Mincerian regression the returns to a year of education rose from about 7.5% in 1980 to about 10% by 1995.


At the same time the quantity of ‘skills’ has increased

Source: Acemoglu (2002, JEL)

Nick Bloom, Stanford University, Labor Topics, 2015

The increase in skills happened both across and within industries

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Autor, Katz and Krueger (1998, QJE)


The skills increase also happened within plants

15Source: Dunne, Haltiwanger and Troske (1997, Carnegie Rochester Conference Series )


The international evidence

SBTC seems to have afflicted both global superpower nations UK US

Other much less important Anglo-Saxon countries (Canada and Australia) also experienced a similar phenomena

Across Europe there has been a more moderate wage experience – but typically more inequality in unemployment

Consistent with the idea that institutions constrained wages in Europe so movements in unemployment occur instead



SBTC caused this change in inequality



What has caused this within and between group changes in inequality? A summary response

(1)Technology changes in much of the 20th century have been skill biased

(2)This SBTC may have accelerated since the 1970s

(3)The supply of skilled workers accelerated in the 1970s but slowed from the 1980s onwards

Thus, skills demand has outstripped supply, particularly since the 1980s,raising between group (high/low education) inequality

The same phenomena has also probably also occurred for unmeasuredskills, raising within group inequality from 1970s onwards


Why has technology been skilled biased (1/2)?

There is no need for technological changes to be skill biased

• The industrial revolution in England increased the use of factories employing low skilled workers at the expense of craftsmen

• Luddite rebellions of 1811 and 1812 were in response to falling wages of skilled weavers as factories replaced traditional weaving

Ned Ludd – probably a fictional character but the movement was a major issue for the British, and even during the Napoleonic wars required extensive troops to surpress


Why has technology been skilled biased (2/2)?

The support for 20th Century SBTC is empirical – there has been a massive increase in the supply of skills (educated workers) at the sametime as skilled wages has risen, at least since 1970s.

This has happened in every sector of the economy – so a universal rise inboth the quantity and price of skills. This must be a demand shift

Evidence that SBTC driven earlier in the century due to electrification(Goldin & Katz, 1998 & 2007)


Over the 20th century skills premia has fluctuated

Source: Goldin & Katz (2007)

Variation in returns mainly due to change in relative supply of skilled and unskilled workers


In fact “computerization” has a long history

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And is now so central because it is 40% of capital investment

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There have actually been 2 technological revolutions: The Green Revolution and the Industrial Revolution

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Back to the increase in the returns to skills – how should we model this?

The traditional Solow model is skill neutral in technical change:Y=AKαLβHγ

But the prior evidence suggests a strong skill biased component.



Can extend the Solow model to skilled and unskilled laborL=[(AsLs)σ + (AuLu)σ]1/σ <1

SBTC in this setup would be the ratio As/Au rising over time

Can substitute into a production function & re-arrange in terms of wage premium. Katz and Murphy (1992, QJE) did this and estimated the following regression implied by this production function:

Ln(Ws/Wu)= β0 + β1(LC/LHS) + Dt + et

They found β1≈-2/3 and Dt about 2.5% (2% on figures to 2005)

Suggests that labor supply clearly matters, but there has been a steady trend favoring skilled labor over the last 40 years.


Trends in college/high-school labor supply

Source: Acemoglu and Autor, (2010)

Skill rose strongly in 1970s because:• Vietnam draft laws• Higher education expansion

interacting with post-war baby boom

Can see 1970s rise in skills supply and falls in relative skilled wages against long-run trend


Katz & Murphy (1992) results (updated by AA 2010)

Source: Autor, Katz & Kearney (2008, RESTAT)

Once you detrend skills supply and relative wages the relationship is clear.

Need to interpret cautiously, though, as only about 40 observations with serially correlated errors

So predicted college/high school wage gap from a trend plus college/high-school skills supply looks a good fit

But - need to interpret cautiously, as only about 40 observations with serially correlated errors



SBTC caused this change in inequality



Why did this SBTC occur?


Why did this SBTC occur - summary?

(1)Proximate cause appears to be cheaper capital and/or computers

(2)But why is this skill-biased? Several arguments:a) Skills directly complement physical capitalb) Skills directly complements computer capitalc) Skills needed for rapid change – post 1970s had rapid change

(3)Other factors that appear to play an additional (more minor) role:• Labor market institutions (minimum wage and Unions)• Trade with developing countries, e.g. China

(4)But why did capital (particularly PCs) become cheaper? One view is the direction of technology is endogenous – the rise in skills promoted SBTC to occur


(a) Physical Capital complementarity (1/2)

One plausible idea is that capital is more complementary to skilled labor then unskilled labor.

Krussell, Ohanian, Rios-Rull and Violante (2000, Econometrica)Y=Kα(λ[μKs

ρ + (1-μ)Lsρ ]σ/ρ + (1- λ )Lu

σ)1/σ

If σ>ρ then reductions in the cost of K increase the demand for Ls

Effectively this replaces As/Au with the price of capital


(a) Physical Capital complementarity (2/2)

Krussell et al. (2000) then provide evidence for a long-run fall in the cost of capital providing results for the model matching the data

So neat model and plausible results.

But there is an identification problem as the impact of the cost of capital is killed by a time trend (Acemoglu (2002, JEL), so can not be certain.


Computing has become cheaper

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(b) Computer capital complementarity (1/3)Worker-level evidenceKrueger (1993) shows that people using computers earn higher wages, and this wage premium has increased over time.

Consistent with computers playing an important role, but also with computers proxying unobserved skills – for example DiNardo and Pischke (1997) show similar phenomena is true for pencils.

Computers or pencils?


The impact of a nice and clear title

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(b) Computer capital complementarity (2/3)

Industry level evidenceA number of papers also show that:

• All industries show an increase in skill demand and skill premium• This rise is faster in industries increasing computerization faster

The drawback to this evidence is that:• Unobserved – could have been something else driving both• Increase in computerization in the 1980s also predicts skills

premium increases in the 1960s• R&D also correlated ≈0.8 with computer use Machin & Van

Reenen (1998)

In summary, appears likely computerization is strongly linked with SBTC, but hard to prove definitively


(b) Computer capital complementarity (3/3)

Most recently Autor, Levy and Murnrane (2003) use the Dictionary of Occupational Titles to allocate cognitive and manual repetitive and non-repetitive tasks to jobs

• Idea is repetitive tasks can be replaced by computers, non-repetitive ones can not

• Find that wages and employment in repetitive tasks fallen fastest – leading to a polarization of employment: “lovely and lousy jobs” as christened by Goos and Manning (2008) for the UK



Evidence that employment is polarizing since the early 1990s – employment growth strongest below 30th percentile above the 75th

The polarization of employment (US data)


Source: Acemoglu and Autor (2010, HLE)

The polarization of employment (International data)

Nick Bloom, Stanford University, Labor Topics, 2015 41Source: Acemoglu and Autor (2010, HLE)

The polarization by occupation (US data)


Polarization of US incomes too (1/2)

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Source: Guvenen, Ozkan and Song (2013)


Polarization of US incomes too (2/2)

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Source: Autor and Dorn, (2013, AER)


(c) Skills are needed to deal with change

The Nelson and Phelps (1966) hypothesis is that change is complex and skilled people are better at dealing with this

• The “acceleration hypothesis” • Consistent with evidence that higher skilled employees are

increasingly in demand as firms rapidly changing technologies

Problems are that periods of 1970 to 1995 are associated with sluggish TFP growth – hard to reconcile this with radical technological change

So in summary seems plausible but hard to fully pin down


What about other factors – trade unions?

This almost certainly played a role in the particularly poor performance of the lower earnings quartiles in the 1980s

But problems with being full story:• unions weakened only in the 1980s while the changes in inequality

started in the 1970s• unions only likely to effect lower/middle quartiles, while higher quartiles

is where most of the action was


What about other factors – minimum wage?

Real value of the minimum wage fell throughout the 1980s as this was not indexed and frequently not updated. This almost certainly played a role in particularly poor performance on the lowest quartile in the 1980s.

But problems with MW as a complete story:• MW only started to decline in real-value in 1980s• Other countries – like the UK – had no MW until late 1990s


What about other factors – international trade(1/2) ?

Trade from China and other countries could also play a role? Three issues:

• Magnitudes not big enough to account for size of change (the US is not open enough, at least until recently) Krugman(2008, Brookings)

• High-skilled wages have risen in almost every industry (including all the non-tradable sectors)

• Also trade generally has limited predictive power: e.g. Berman, Bound and Griliches (1994, QJE), Autor, Katz and Krueger (1997, QJE) and Machin and Van Reenen (1998 QJE)


What about other factors – international trade(2/2) ?

But:• Could possibly be due to outsourcing within non-tradable industries

• More generally the empirical evidence is primarily in late 1990s before Chinese imports really took off. Since then entire industries have virtually disappeared (furniture, toys, textiles etc..)

So trade is probably an increasingly big factor: Bloom, Draca and Van Reenen (2011) and Autor, Dorn and Hansen (2013) both finding major effects only post 2000 (particularly 2005).

Also true that manufacturing in particular seen a very sharp drop in employment since 2000 due to China and WTO, and that has high share non-skilled middle-income employees (Pierce and Shott, 2013)


Source: Charles, Hurst and Notowidigdo (2013)49

China joining WTO coincided huge drop in US manufacturing employment


Source: Charles, Hurst and Notowidigdo (2013)50

Masked by the construction boom until 2008 crash


What about other factors – “measurement”

• Maybe educational content in a college degree is rising– US college now harder to get into (greater selection) – Education more effective per year (productivity and

inputs are both rising in education).

• Would suggest that college degree probably increasingly less substitutable with a non-college degree (larger gap in the human-capital between them)

• Evidence (see next slide) suggests this

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Source: “On the Time-Varying Substitutability of Labor Inputs and the Rise of Wage Inequality in the U.S. 1976-2010” by Jay Hong & Raul Santaeulalia-Lopez (2011 WUSTL mimeo)

Elasticity of Substitution college vs non-college(by industry)

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Endogeneous technical change

Final question is why did SBTC occur in the 1970s?

Acemoglu (1998, QJE and 2002 RESTUD) and others have a number of papers around the idea of endogenous technical change – idea that increased supply of graduates led to technical change

Related idea is endogenous technical adoption – different countries adopt different technologies endogenously

An interesting area of research and plausible hypothesis but little empirical evidence beyond particular examples like: - drugs (Acemoglu and Linn, 2004 QJE) - air-conditioners (Newell, Jaffe and Stavins, 1999 QJE) - clean-tech spurred on by recent rise in oil prices


Next lecture on top-end pay

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BACK-UP


Also an interesting sharp-post war contraction in inequality – the “Great Compression”

Goldin and Margo (1992) argue arises because of:• Supply: Increased

university enrollment (GI Bill),

• Demand: Increase in non-skilled labor demand from manufacturing

• Institutional: Unions strong post-war (low unemployment) and National War Labor Board

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